Resistive memory device and method for fabricating the same

ABSTRACT

A resistive memory device includes a lower electrode formed on a substrate, a resistive layer formed on the lower electrode, and an upper electrode on the resistive layer, wherein a lower portion of the upper electrode is narrower than an upper portion of the upper electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/979,922 filed on Dec. 28, 2010, which claims priority of KoreanPatent Application No. 10-2010-0005549, filed on Jan. 21, 2010. Thedisclosure of each of the foregoing application is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

Exemplary embodiments of the present invention relate to a semiconductordevice fabrication technology, and more particularly, to a resistivememory device using a resistance change in detecting data, such as anonvolatile resistive random access memory (ReRAM) and a method forfabricating the same.

Next generation memory devices which can replace a dynamic random accessmemory (DRAM) and a flash memory are being developed. One of such nextgeneration memory devices is a resistive memory device using a resistivelayer. Specifically, a resistive memory device uses a material whoseresistance rapidly changes according to a bias applied thereto and thuscan switch between at least two different resistance states.

According to an example, a resistive memory device includes a resistiveelement and a selection element. The resistive element includes a lowerelectrode, a resistive layer, and an upper electrode, which aresequentially formed on a substrate. A filament current path is formed orremoved within the resistive layer of the resistive element according tobiases applied to the upper electrode and the lower electrode, and datais stored according to a resistance state which depends on the formationand removal of the filament current path.

Therefore, the resistive memory device may have a large sensing currentand may be sensitive to a resistance. Here, as the effective area of theresistive element becomes larger, a characteristic of the resistiveelement is degraded. Thus, methods for reducing the effective area ofthe resistive element are useful.

Reducing an area of a resistive element is difficult. Further, inreducing the area of the resistive element, the area of the selectionelement may also be reduced and thus the resistance of the selectionelement may be increased. Therefore, an electric field and a currentrequired upon a switching operation may not be appropriately supplied tothe resistive element.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a resistive memorydevice including an upper electrode a lower portion of which is narrowerthan an upper portion thereof.

Another embodiment of the present invention is directed to a resistivememory device includes: a lower electrode formed on a substrate; aresistive layer formed on the lower electrode; and an upper electrodeformed on the resistive layer, wherein a lower portion of the upperelectrode is narrower than an upper portion of the upper electrode.

In accordance with an embodiment of the present invention, a method forfabricating a resistive memory device includes: forming a lowerelectrode on a substrate; forming a sacrificial layer on the lowerelectrode; etching the sacrificial layer to form a trench having a lowerportion narrower than an upper portion of the trench; forming aresistive layer in the trench; and forming an upper electrode by buryinga conductive layer within the trench and over the resistive layer formedin the trench.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F are cross-sectional views illustrating a method forfabricating a resistive memory device in accordance with a firstembodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views illustrating a method forfabricating a resistive memory device in accordance with a secondembodiment of the present invention.

FIGS. 3A to 3C are cross-sectional views illustrating a method forfabricating a resistive memory device in accordance with a thirdembodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The drawings are not necessarily to scale and in some instances,proportions may have been exaggerated in order to dearly illustratefeatures of the embodiments. When a first layer is referred to as being“on” a second layer or “on” a substrate, it not only refers to a casewhere the first layer is formed directly on the second layer or thesubstrate but also a case where a third layer exists between the firstlayer and the second layer or the substrate.

FIGS. 1A to 1F are cross-sectional views illustrating a method forfabricating a resistive memory device in accordance with a firstembodiment of the present invention.

Referring to FIG. 1A, a selection line 11 is formed on a substrate 10.The selection line 11 may be formed of a diffusion barrier materialselected from copper, aluminum, tungsten, ruthenium, platinum, gold,titanium nitride, and tantalum nitride. For example, the selection line11 may be formed of copper or tungsten. In addition, the selection line11 may be formed by forming a conductive layer and patterning theconductive layer, or may be formed by a damascene process.

A lower electrode 12 is formed on the selection line 11. The lowerelectrode 12 may be formed of a diffusion barrier material to selectedfrom nickel, platinum, gold, silver, copper, tungsten, titanium nitride,tantalum nitride, aluminum, and ruthenium.

A sacrificial layer is formed on the lower electrode 12. The sacrificiallayer is formed to ensure a region in which a resistive layer and anupper electrode are to be formed in a subsequent process. Thesacrificial layer may be formed by stacking a desired material layer.

In the prefer embodiment, a first hard mask layer 13 is formed on thelower electrode 12, and an insulation layer 14 is formed on the firsthard mask layer 13. In this manner, the sacrificial layer including thefirst hard mask layer 13 and the insulation layer 14 may be formed. Thefirst hard mask layer 13 may include silicon nitride or siliconoxynitride which has excellent insulation characteristic.

A second hard mask layer 40 is formed on the sacrificial layer 13 and14, and a photoresist pattern 16 is formed on the second hard mask layer40. The photoresist pattern 16 is formed to have an opening which opensa region in which a resistive element pattern is to be formed, in orderto form a pattern of the resistive element.

Referring to FIG. 1B, the second hard mask layer 40 is etched using thephotoresist pattern 16 as an etch barrier, and the sacrificial layer 13and 14 are etched using the etched second hard mask layer 40 as an etchbarrier. Through such an etching process, a first trench T1 for aresistive element pattern is formed.

At this time, the etching process is performed to expose the surface ofthe lower electrode 12 under the first trench Ti. An overetching processmay be performed in order to ensure a sufficient contact area between aresistive layer to be formed by a subsequent process and the lowerelectrode 12. That is, when forming the first trench T1, the lowerelectrode 12 may be etched by a desired depth.

In FIG. 1B, a reference numeral “12A” represents the lower electrode thesurface of which is partially etched by the overetching process. Inaddition, a reference numeral “14A” represents the insulation layeretched in the process of forming the first trench T1, and a referencenumeral “13A” represents the etched first hard mask layer.

The remaining photoresist pattern 16 and second hard mask layer 40 areremoved.

Referred to FIG. 1C, the insulation layer 14A exposed at the inner wallof the first trench T1 is recessed by a desired thickness to increasethe upper width of the first trench Ti, The process of recessing theinsulation layer 14A may be performed under a condition where an etchselectivity between the insulation layer 14A and the first hard masklayer 13A is high. That is, the upper width of the first trench T1 maybe increased by selectively etching the insulation layer 14A by adesired thickness while the first hard mask layer 13A remains (that is,the etching rate of the insulation layer 14A is higher than that of thefirst hard mask layer 13A).

For example, the insulation layer 14A may be recessed by a to dryetching process or a wet etching process. According to an example, theinsulation layer 14A may be recessed by an isotropic etching process.

Consequently, a second trench T2 is formed to have a lower portionnarrower than an upper portion thereof (W1<W2). That is, the secondtrench T2 is formed to have a stepped sidewall, a width of which isnarrower at the lower portion thereof. In FIG. 1C, a reference numeral“14B” represents the recessed insulation layer.

Referring to FIG. 10, a resistive layer 15 is formed over a profile ofthe second trench T2. The resistive layer 15 is formed of any reasonablysuitable material that causes a resistance change. In the preferembodiment, the resistive layer 15 comprises phase change materials fora PCRAM or resistive variable materials for an ReRAM. For example, theresistive layer 15 may include a chalcogenide glass, a binary transitionmetal oxide, or a perovskite oxide.

A conductive layer 17 for an upper electrode is formed over a resultingstructure in which the resistive layer 15 has been formed. According toan example, the conductive layer 17 for the upper electrode may includea diffusion barrier material selected from nickel, platinum, gold,silver, copper, tungsten, titanium nitride, tantalum nitride, aluminum,and ruthenium.

The resistive layer 15 and the conductive layer 17 for the upperelectrode may be formed by a process having excellent step coverage. Forexample, the resistive layer 15 and the conductive layer 17 for theupper electrode may be formed by a chemical vapor deposition (CVD)process or an atomic layer deposition (ALD) process.

Referring to FIG. 1E, an upper electrode 17A is formed by performing aplanarization process until the surface of the insulation layer 14B isexposed. In FIG. 1E, a reference numeral “15A” represents the resistivelayer etched during the planarization process. The upper electrode 17Amay be formed in a pillar shape in which a lower portion is narrowerthan an upper portion. In particular, the upper electrode 17A may beformed to have a stepped sidewall, a width of which is narrower at thelower portion thereof.

In addition, the sidewall and the lower portion of the upper electrode17A are surrounded by the resistive layer 15A. Therefore, the resistivelayer 15A is disposed between the upper electrode 17A and the lowerelectrode 12A. In this manner, the resistive element including the lowerelectrode 12A, the resistive layer 15A, and the upper electrode 17A, alower portion of which is narrower than an upper portion thereof, isformed.

Referring to FIG. 1F, the upper electrode 17A and the resistive layer15A buried within the trench are partially recessed by a desired depth.In FIG. 1F, a reference numeral “17B” represents the upper electrodeetched by the recess process, and a reference numeral “15B” representsthe etched resistive layer.

Through the recess process, the upper electrode 17B and the resistivelayer 155 are buried within the sacrificial layer 13A and 145 to on thelower electrode 12A. At this time, the top surfaces of the upperelectrode 175 and the resistive layer 155 are lower than the top surfaceof the sacrificial layer 14B.

A selection element 18 is formed on a resulting structure in which theupper electrode 17B and the resistive layer 15B are partially recessedby a desired depth. The selection element 18 may include apolycrystalline silicon diode, an oxide diode, a thin tunnel oxidelayer, or a thin tunnel nitride layer.

A selection electrode 19 is formed on the selection element 18.

The selection electrode 19 may be formed of a diffusion barrier materialselected from nickel, platinum, gold, silver, copper, tungsten, titaniumnitride, tantalum nitride, aluminum, and ruthenium.

In accordance with the embodiment of the present invention set forthabove, the upper electrode 17B, a lower portion of which is narrowerthan an upper portion thereof, can be formed. By forming the upperelectrode 17B, a lower portion of which becomes narrower in width, theeffective area W3 of the resistive element is further reduced, therebyobtaining appropriate characteristics of the resistive memory device. Inaddition, by forming the upper electrode 17B, an upper portion of whichbecomes wider in width, the contact area between the selection element18 and the upper electrode 176 of the resistive element (that is, theeffective area W4 of the selection element 18), can be furtherincreased. Therefore, since the resistance of the selection element 18for turning on a connection to the resistive element is reduced, anelectric field and a current required in the operation of switching theresistive element can be appropriately supplied.

FIGS. 2A and 26 are cross-sectional views illustrating a method forfabricating a resistive memory device in accordance with a secondembodiment of the present invention.

Referring to FIG. 2A, a selection line 21 is formed on a substrate 20,and a lower electrode 22 is formed on the selection line 21. Sacrificiallayers 23 and 24 are formed on the lower electrode 22. The sacrificiallayers 23 and 24 are etched to form a trench, a lower portion of whichis narrower than an upper portion thereof. A resistive layer 25 isformed on a resulting structure in which the trench has been formed, Aconductive layer for an upper electrode is formed on a resultingstructure in which the resistive layer 25 has been formed.

An upper electrode 26 is formed by performing a planarization processuntil the surface of the sacrificial layer 24 is exposed. The upperelectrode 26 and the resistive layer 25 are buried within thesacrificial layers 23 and 24 and buried over the lower electrode 22. Atthis time, the top surfaces of the upper electrode 26 and the resistivelayer 25 are equal in height to the top surface of the sacrificial layer24.

Since the preceding processes are substantially identical to the firstembodiment described with reference to FIGS. 1A to 1E, detailed todescription thereof will be omitted.

Referring to FIG. 2B, a selection element 27 is formed on a resultingstructure in which the planarization process has been performed. Aselection electrode 28 is formed on the selection element 27.

FIGS. 3A to 3C are cross-sectional views illustrating a method forfabricating a resistive memory device in accordance with a thirdembodiment of the present invention.

Referring to FIG. 3A, a selection line 31 is formed on a substrate 30,and a lower electrode 32 is formed on the selection line 31. Sacrificiallayers 33 and 34 are formed on the lower electrode 32. The sacrificiallayers 33 and 34 are etched to form a trench, a lower portion of whichis narrower than an upper portion thereof. A resistive layer 35 isformed on a resulting structure in which the trench has been formed, Aconductive layer for an upper electrode is formed on a resultingstructure in which the resistive layer 35 has been formed. An upperelectrode 36 is formed by performing a planarization process until thesurface of the sacrificial layer 34 is exposed. In this manner, theupper electrode 36 is formed. At this time, the sidewall and bottomsurface of the upper electrode 36 are surrounded by the resistive layer35.

Since the preceding processes are substantially identical to the firstembodiment described with reference to FIGS. 1A to 1E, detaileddescription thereof will be omitted.

Referring to FIG. 3B, an etching process is performed so that an upperportion of the upper electrode 36 protrudes. In FIG. 3B, a referencenumeral “36A” represents the upper electrode, an upper portion of whichprotrudes by the etching process, and a reference numeral “35A”represents the etched resistive layer. In addition, a reference numeral“34A” represents the etched sacrificial layer.

For example, the etching process may be performed under a condition thatan etch rate of the sacrificial layers 33 and 34A and the resistivelayer 35A is higher than that of the upper electrode 36A. According toan example, the etching process may be performed by an anisotropicetching process (see arrows of FIG. 3B),

Due to such an etching process, the sacrificial layers 33 and 34A andthe resistive layer 35A are partially etched by a desired depth so thatthe upper portion of the upper electrode 36A protrudes. That is, whilethe upper electrode 36A and the resistive layer 35 a are buried withinthe sacrificial layers 33 and 34A, the top surface of the upperelectrode 36A protrudes over the top surfaces of the resistive layer 35Aand the sacrificial layer 34A. In addition, the upper edge {circlearound (1)} of the protruding upper electrode 36A is etched to berounded as shown in FIG. 3B.

In this manner, the upper electrode 36A having a profile with a roundedupper edge is formed. Here, the resistive element including the lowerelectrode 32, the resistive layer 35A, and the upper electrode 36A isformed where a lower portion of the upper electrode 36A is narrower thanan upper portion thereof and an upper edge of the upper electrode 36Ahas a rounded profile.

Referring to FIG. 3C, a selection element 37 is formed on a resultingstructure in which the upper portion of the upper electrode 36Aprotrudes. A selection electrode 38 is formed on the selection element37.

In accordance with the embodiment set forth above, after forming theprotruding upper electrode 36A, the selection element 37 is formed onthe protruding upper electrode 36A. Thus, the effective area of theselection element 37 for contact can be further increased. In addition,since the upper edge of the upper electrode 36A has a rounded profile,an electric field may be prevented from being concentrated on the edgeof the upper electrode 36A. Therefore, an appropriate switchingcharacteristic distribution of the resistive element may be obtained,and occurrence of a leakage current may be prevented/reduced at the edgeof the resistive element. Furthermore, an appropriate on/off ratio(e.g., resistance ratio) of the selection element may be obtained.

In accordance with the embodiments of the present invention, since anupper electrode is formed to have a lower portion narrower than an upperportion thereof, the effective area of the resistive element is reducedand the effective area of the selection element is increased. Thereduction in the effective area of the resistive element decreases anamount of a current required in a switching operation so thatappropriate characteristics of the resistive memory device may beobtained. Furthermore, since the effective area of the selection elementis increased, the resistance thereof is reduced, whereby an electricfield and a current can be appropriately supplied to the resistiveelement during a switching operation.

While the present invention has been described with respect to thespecific embodiments, it v rill be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A resistive memory device comprising: a lowerelectrode formed over a substrate; a sacrificial layer formed over thelower electrode; a resistive layer buried in the sacrificial layer overthe lower electrode; and an upper electrode formed over the resistivelayer, wherein a top surface of the upper electrode protrudes higherthan top surface of the resistive layer and the sacrificial layer, andwherein the top surface of the upper electrode has a rounded profile. 2.The resistive memory device of claim 1, further comprising: a selectionelement fanned on the upper electrode; and a selection electrode formedon the selection element.
 3. The resistive memory device of claim 1,wherein the upper electrode has a pillar shape in which a lower portionis narrower than an upper portion and the resistive layer surrounds asidewall and the lower portion of the upper electrode.
 4. The resistivememory device of claim 3, wherein the upper electrode has a steppedsidewall having a width that is narrower at a lower portion thereof. 5.The resistive memory device of claim 1, wherein a height of the topsurface of the resistive layer is the same as a height of the topsurface of the sacrificial layer.
 6. The resistive memory device ofclaim 1, wherein the entire top surface of the upper electrode protrudesabove the entire top surfaces of the resistive layer and the sacrificiallayer.
 7. The resistive memory device of claim 1, further comprising: aselection element over the upper electrode; and a selection electrodeover the upper electrode, wherein the selection element and theselection electrode are configured to select the resistive memory deviceformed by the lower electrode, the resistive layer, and the upperelectrode.
 8. The resistive memory device of claim 7, wherein theselection of the resistive memory includes turning on a connection tothe resistive memory.
 9. The resistive memory device of claim 1, whereinthe resistive layer comprises phase change materials or resistivevariable materials.
 10. A resistive memory device comprising: a lowerelectrode formed over a substrate; a resistive layer formed over thelower electrode; and an upper electrode formed over the resistive layer,wherein a lower portion of the upper electrode is narrower than an upperportion of the upper electrode, and a top surface of the upper electrodehas a rounded profile.